1. Field of Use
This invention relates generally to multisection telescopic crane booms having rotatable screws for extending and retracting the boom sections thereof and, in particular, to driving and support means for such screws.
2. Description of the Prior Art
In conventional multisection telescopic crane booms, such as are used on mobile cranes or the like, it is well known to employ extendable/retractable elongated hydraulic cylinder units interconnected between relatively movable boom sections to extend and retract the boom. As telescopic booms increase in size and weight and in the number of movable sections, the size, weight, number and complexity of hydraulic cylinders increase accordingly. It is desirable therefore to provide other improved means to operate relatively large telescopic booms.
U.S. Pat. No. 3,326,391 discloses a manually operated portable load handling swinging crane of relatively small size for handling moderate loads and which comprises two telescopically movable hollow parts including an extension part which is telescopically extendable and retractable relative to a main part by means of a manually rotatable single elongated screw which has its base end rotatably supported on the base end of the main part and engages a threaded insert fixed to the base of the extension part.
U.S. Pat. No. 4,062,156 discloses a four-section vertically disposed extendable small "rod", such as a car radio antenna having three movable sections which telescope within a housing and wherein a motor driven, rotatable single elongated screw which has its base end rotatably supported on the base end of a housing engages a threaded member on the base end of each of the three movable sections.
U.S. Pat. No. 3,296,757 shows a multi-section telescopic vertical mast wherein an exteriorly-located manually or motor-driven rotatable screw connected between a lowermost housing section and a topmost section effects telescopic movement of all movable sections, as one section acts upon another to effect axial movement.
Norwegian Pat. No. 23666 (1913) shows arrangements similar to U.S. Pat. No. 3,296,757 and U.S. Pat. No. 4,062,156.
German Pat. Nos. 289,534 (1913) and 295,440 (1913) show multi-section vertically disposed telescopic masts wherein a plurality of manually operated screws, one driven by another, are employed to extend and retract movable mast sections but the screw arrangements are such that not all movable sections can telescope within the base section, as German Pat. No. 295,440 makes clear in FIG. 2.
U.S. Pat. Nos. 3,082,607; 1,342,828 and 1,286,807 show other telescopic mast arrangements.
U.S. Pat. Nos. 4,125,974; 4,098,172; and 4,094,230 show arrangements for supporting hydraulic cylinders in telescopic booms.